1. Field of the Invention
The present invention relates to a scroll compressor, and in particular to a scroll compressor suitable for a vapor compression refrigerating cycle that uses a refrigerant having the supercritical region of carbon dioxide (CO.sub.2), for example.
2. Description of the Related Art
Recently, a refrigeration cycle using carbon dioxide (referred to hereinbelow as a "carbon dioxide cycle") as a working gas (refrigerant gas) has been proposed, for example, in Japanese Examined Patent Application, Second Publication, No. Hei 7-18602, as one measure for eliminating the use of Freon (dichlorofluoromethane) as a refrigerant in the vapor compression-type refrigerating cycle. This carbon dioxide cycle is identical to the conventional vapor compression-type refrigerating cycle that uses Freon. That is, as shown by A-B-C-D-A in FIG. 5, which shows a carbon dioxide Mollier chart, the carbon dioxide in the gaseous phase is compressed by a compressor (A-B), and this gas-phase carbon dioxide that has been compressed to a high temperature is cooled in a radiator, such as a gas cooler (B-C). Next, the carbon dioxide is decompressed using a decompressor (C-D), the carbon dioxide that has changed to a liquid phase is vaporized (D-A), and an external fluid such as air is cooled by removing its latent heat of vaporization.
However, the critical temperature of carbon dioxide is about 31.degree., which is low compared to the critical temperature of Freon, the conventional refrigerant. When the external temperature is high, during summer, for example, the temperature of carbon dioxide on the radiator side is higher than its critical temperature. This means that the carbon dioxide does not condense at the radiator outlet side. In FIG. 5, this is shown by the fact that the line BC does not cross the saturated liquid line SL. In addition, the state on the radiator output side (point C) is determined by the discharge pressure of the compressor and the temperature of the carbon dioxide at the radiator outlet side. Moreover, the temperature of the carbon dioxide at the radiator outlet side is determined by the radiating capacity of the radiator and the temperature of the uncontrollable external air. Due to this, the temperature at the radiator outlet cannot be substantially controlled. Therefore, the state of the radiator outlet side (point C) can be controlled by the discharge pressure of the compressor, that is, the pressure on the radiator outlet side. This means that in order to guarantee sufficient refrigerating capacity (difference in enthalpy) when the temperature of the external air is high, during summer, for example, as shown by E-F-G-H-E, the pressure on the radiator output side must be high. In order to attain this, the operating pressure of the compressor must be high in comparison to the refrigeration cycle used with conventional Freon. In the case of an air conditioning device for an automobile, for example, the operating pressure of the compressor when using Freon (Trademark R134) is about 3 kg/cm.sup.2, while in contrast, this pressure must be raised to about 40 kg/cm.sup.2 for carbon dioxide. In addition, the operation stopping pressure when using Freon (Trademark R134) is about 15 kg/cm.sup.2, while in contrast it must be raised to about 100 kg/cm.sup.2 for carbon dioxide.
Below, referring to FIG. 6, a typical scroll compressor as disclosed in Japanese Unexamined Patent Application, First Publication, No. Hei 5-149270, will be explained. As shown in FIG. 6, in a casing (not illustrated), a fixed scroll member 100, an orbiting scroll member 101, and an eccentric axle 102 are provided.
The fixed scroll 100 is formed by an end plate 100a providing a discharge port for discharging the compressor working gas (not illustrated) and an involute wrap 106b provided on one face of this end plate 100a.
The orbiting scroll 101 is formed by an end plate 101a comprising an involute wrap side end plate 105 and an eccentric axle side end plate 106, an involute wrap 101b provided on the face of the involute wrap side end plate 105 facing the end plate 100a of the fixed scroll, and an engagement part 103 provided on the face of the eccentric axle side end plate 106 not facing the involute wrap side end plate 105, and accommodating therein the eccentric axle 102, described below. The involute compression chamber 104 is formed by installing the fixed scroll 100 and the orbiting scroll 101 in the casing such that the involute wrap 100b of the fixed scroll 100 and the involute wrap 101b of the orbiting scroll 101 intermesh. Thereby, when the orbiting scroll 101 is rotated eccentrically with respect to the fixed scroll 100 by rotating the eccentric axle 102 installed in the engagement part 103, while the working gas in the casing is compressed in compression chamber 104, the working gas can be discharged from the discharge port provided on the end plate 100a of the fixed scroll 100.
Moreover, as explained above, a scroll compressor using carbon dioxide as a working gas requires a high revolution and pressure. Thus, there is a concern of a deterioration in capacity due to leakage of the working gas. In order to prevent this, the orbiting scroll 101 presses against the fixed scroll 100. That is, along the axial direction of the orbiting scroll 101, the end plate 100a thereof is divided into an involute wrap side end plate 105 providing an involute projection 10b and an eccentric axle side end plate 106 providing an engagement part 103. In addition, an sealed space 107 is formed between the involute wrap side end plate 105 and the eccentric axle side end plate 106. Furthermore, on the involute wrap side end plate 105, a narrow hole 108 is formed for introducing the high pressure working gas in the compression chamber 104 into the sealed space 107. Moreover, in FIG. 6, reference numeral 109 denotes a seal part for sealing the sealed space 107.
By adopting this kind of structure, one part of the high pressure working gas in the compression chamber 104 is introduced into the sealed space 107 via the narrow hole 108, and fills the sealed space 107. When comparing the upward force operating from the sealed space 107 on the involute wrap side end plate 105 and the downward force operating from the compression chamber 104 on the involute wrap side end plate 105, the upward force is greater than the downward force, and thus the involute wrap side end plate 105 rises up as a whole and presses against the fixed scroll 100 side. Therefore, the end plate 100a of the fixed scroll 100 and the end plate 105 of the orbiting scroll 101 are on intimate contact. Thus, gas leakage from between the fixed scroll 100 and the orbiting scroll 101 is inhibited.
However, in the above-described conventional scroll compressor, the revolution of the eccentric axle side end plate 106 of the orbiting scroll 101 must be transmitted to the involute wrap side end plate 105 via the above-described seal member 109. Thus, there is the problem of low transmission efficiency.
Thus, the friction on the seal member 109 becomes severe, and there is the problem that the operation of replacing the seal member 109 requires labor.
Furthermore, as described above, in the conventional scroll compressor, a compressed working gas is used, and the involute wrap side end plate 105 is pressed against the fixed scroll 100 side. However, in particular during operation of the scroll compressor, the compression or the working gas does not become sufficiently high, and thus the force pushing the involute wrap side end plate 105 against the fixed scroll 100 is weak and the compression efficiency is low.
In consideration of the above-described problems, it is an object of the present invention to provide a scroll compressor that transmits rotation of the eccentric axle side end plate 106 of the orbiting scroll to the involute wrap side end plate 105 with good efficiency, and sufficiently presses the involute wrap side end plate 105 continuously against the fixed scroll 100 without causing friction with the seal member 109.